1. Field of the Invention
The present invention relates to a class of metallocene compounds, to a catalyst for the polimerization of olefins comprising said metallocenes and to processes for the polimerization of olefins carried out in the presence of said catalyst.
The invention also relates to processes for the preparation of the ligands of said metallocenes, as well as to a class of novel bridged ligands.
2. Description of the Prior Art
Metallocene compounds are known which are active as catalyst components in the olefin polymerization reactions.
European patent application EP-A-35 242, for instance, discloses a process for the polymerization of ethylene and propylene in the presence of a catalyst system comprising (a) a cyclopentadienyl compound of a transition metal and (b) an alumoxane.
European patent application EP-A-129 368 discloses a catalyst system for the polymerization of olefins comprising (a) a mono-, bi- or tri-cyclopentadienyl coordination complex with a transition metal and (b) an alumoxane. With this catalyst it is possible to prepare polyolefins of controlled molecular weight.
European patent application EP-A-351 392 discloses a catalyst, which can be used in the preparation of syndiotactic polyolefins, comprising a metallocene compound with two cyclopentadienyl based rings linked with a bridging group in which one of the two cyclopentadiene rings is substituted differently from the other. The preferred compound indicated is isopropylidene(fluorenyl)(cyclopentadienyl)hafnium dichloride.
EP-A-604 908 discloses a class of bis-fluorenyl compounds bridged with a one-atom-bridge. These metallocenes are useful as catalyst components for the polymerization of olefins and, expecially, for the preparation of high molecular weight atactic polypropylene.